Switching circuit



y 1.5, 1952 r w. H. BURKHART ET AL 2,603,746

SWITCHING CIRCUIT Filed Oct. 15, i950 FIG. 3

: i l v I INVENTORS WILLIAM H BUR/(HART AM/R H. SEPAHBAN v ATTORNEYPatented July 15, 1952 .zsgm'rE s ATEN FFICE I I I is v vironmd amour-rn I i I .Burkhart .and Aniir ,-Hassan Sepahbamj; East Orange, N, fJ.,'assignors 'to Monroe Calculating Mac hine Company, N Orange, N. 'J.,-acorporation of'Delaware I i uti e October '13, 1959, manna-189,922

in electronic digital computing machines in whichthe binary or codeddecimal system of computation is used.

According to this invention, two or more incoming variable potentialsare combined through resistances of selected values and are-thenimpressed upon the single;gr-id-=ofantriode to control conductivity ofthe tube andthereforeythe output of the tube. The output oranode-circuitv may be coupled to a subsequent stage or, stages and itincludes a voltage divider, the resistance values of which are soselected and adjusted with respect to the tube characteristics,particularly gain and cut-01f, that it enablesa further stage tobecontrolled with the same voltage swing on its control grid as issupplied to the first stage. In other words, the two values, high andlow, of the inputs are substantially matched in. the output.

Accordingly, it is amongthe objects of this invention to provide anelectronic circuit for delivering an output which may be heldat one oftwo voltage levels dependent; on whether theapplied input signals arecombined at the higher of said levels,.that being above cut-offpotential, or whetherthe resultant input is of any potential belowcut-off. v

Another object is means for combining the effects of n binary inputvariables, a, b, c, n, each'of which will have at a giveninstant eitherone or the other, of two potentials e1 and 62, where 61 is more positivethan a cut-off potential cc and c2 is more negative than ec, said meansbeing capable of delivistill another object is to provide the meansforjcomposing an electronic system whichshall have a plurality ofidentical units or .building blocks, such as described in thetwopreceding. paragraphs, where concatenatedcontrol of the units from stageto stage may be obtained withto provide electronic gating positivevandone negative p'owersupply out attenuation of the output voltage andwithout appreciable back effect on the, first unit.

It .is among the features of this invention to employ triodevacuum tubesor the equivalent rather than multigrid tubes, as commonly usedwhenthere are two or more inputs for any one tube However miniature twintriode tubes may beused to' .efie'ct economy of space and cost". One issufe The objects as above mentioned are achieved through a choiceofjcomponents of the building block and 1 through advantageous synthesizingof thesel block's forv'arious ultimate purposes such adder.,Numerousother applications may read ily', be developed by thoseskilledin the art.

Inelec'tronic computing machines which deal with 'binary'numbers,thedigit l may arbitrarily be represented by a'volta'ge 61 equal to 0volts,

fo'r example. 'fThe digit 0 may also arbitrarily be representedby avoltage ez equal to 20 vows,

for example. As will be shown hereinafter, a

practical circuit arrangement for use as'abinary adder. may have suchother characteristics as would render this choice of values for'ei andcz' dependable andotherwise desirable, though other values may readilybeselected to meet individual requirements of a circuit and its operatingcom ponents. 1 "For a better understanding of this invention referencewill now be made to the accompanying drawings, in which: v

Fig. 1 is a basic electronic switching circuit-in which two variables(inputs),.such as potentials representative-of two binary numbers, aremade applicable for joint control of a single grid of )a triode, todeliver one or: the other of two output potentials having the same rangeof variation as the input potentials; v

I Fig.2;shows a modification of part of thelcircuitof'Fig. 1-;' I Fig. 3shows how the circuit ofFig. 1 or of Fig.2 may be expanded to-providejoint control of a triodetube by Variable inputs;

Fig. 4 shows an arrangement of a pluralityof;

triode tubes having their anodes parallel-connected, so that the commonoutput shall be high or low, depending on whether, in the case of onlytwo tubes (a) both tubes are nonconductive, or lb) one or both tubes areconductive; and

Fig. shows an arrangement of seven triodes having the same oresimilarcircuit parameters with respectto thevtriode of Fig, 1,]this arrangementbeing suitable for'i'use as a 'onef stagefunit for digital addition orsubtraction'of binarynumbers.

The basic unit, or v Fig; 1 will first be described' The triodedischargetube l has its cathode grounded and its anode is connected througharesistor .2 to the positive terminal of a directlcurrent sourcedelivering potentials of +100 voltsl and movolts r and having a groundedneutral, or 0-volt termi- 4 is, either a twin triode connected forflip-flop operation, or a gaseous discharge tube with hot or coldcathode. The signals may result from the read-out of data stored on amagnetic tape or drum. They may be derived from pulse keying of aperforated tape, or other memory device. In the operation of the tube,stageshown in 'Fig. 1 let it be assumed that a low voltage out- I put e2is desired when the input signals a, and b a building block shown in areboth high and that a high voltage output 61 is desired when either orboth of the input signals is of low voltage.

It will be apparent that,

"disregarding the effect of grid'current, the grid mil. The negativeterminal of this source is also '5 a connected to the anode of the tubethrough voltagedivider resistors 3 and 4. An output lead or utilizationcircuit 5 isconnected to the junctionbetweenr'esistorsii and 4. e 7 I rI Twofi'nput'potentials; a and b are to be'fed' simultaneously to thegrid of tube I through resistors 6 and 1 respectively.v Each ofthese input potentials, which are mutually independent;

may have a value e1 or e72, representative, for examplaof thebinarydigits land 0 respectively,

Qr, if the switching unit i sito'be used in a system dealing withsymboliclogic', er may represent a, statement and rezmay represent thenegation of' thatist'atement. Symbolici logic deals with statements andwordsg'such as {and,,or, not, same,

different, some, all. a Theprinciple of this invention will, however, beQsumcintIy explained by confiningfurther description mostly to itsmathematicaluses. v p

The following input and output potentials have provenpractical forelectronic computers: e1=0 volts andez=-20 volts. These potentials willbe'understood to meet the requirements of our building block! having thecircuit parameters as shown, although it will be apparent that varia-'tions in the values of the circuit elements may dictatesomewhatidifferent signal potentials,

On the assumption'that a standard double triode tube such as 12AU'7 isto be used, then the resistor values which wehavefound particularly well:suited to our requirements are as follows;

and will be taken as'circuit parameters for each half; of the twintriode, theother half being considered a duplicate building block whichwould have its-own similar circuit componentlsg Ohms Resistori 2 18,000'Resisto'r' 3 65,000 Resistor'f' 4?;000 Resistors" 6 and 1; (each)100,000

:Thesexresistor-values have been chosen with the object of insuring thatthe output'potential shall be equal to one of the input potentials ve1orezdependin on whether the combined effect ofcthose inputnpotentials isto render thetube conductive or to biasit below cut-ofi "The cut- Vofipo'tential of tube 12AU7 is -76 volts when powered with "the anodepotentialas shown.

a When a tube stage such as that ofFig. l is to r be oneof severalconcatenated stages}; it is ole sirable'that' the resistances of theinput'couplings be high with respect to the impedance offthe drivingcircuit.

The input signals may be derived from any suitable source or sources,not show'n. Such a source, for example, may be'a trigger tube; thatw'ill jbeat '0 volts if both signals, a and b are at 0 volts. Then 'thetube I will be conductive and its output lead -5 will have the potentialV82- -20 v. The tube will otherwise be non-conductivesince, ifboth-signals a and b are at 20 v.,

the grid will be at -20 v., which is far below cut-off; or, if only oneof the signals a and b is at .20 v., the grid will be at 10 v. whichalso is below the cut-offlevel *6 v. In either case,

theoutput will be e1 0 volts. e I p v The several results of operationas described in The above'table shows that gating operations, may beperformed either when the circuitis to be used in mathematical work orin dealing with problems of'symboliclogic.

Fig. 2 shows a triode having its cathode connected to the direct-currentoperating source :to give it a'potential of -12 v. with respect toground. in other respects the tube has circuit components correspondingwith those of Fig. 1'. When the cathode is negatively biased in thisway, the same potentials c1 and 62 may be used for signal input as inthe case of :Fig. l, but the results willbe different. When a negativebias of 12 volts is appliedfto the cathode oftube 8 (Fig. 2) and thesame input potentials er and (2; are applied as before, thecut off biasthen becomes +18 volts, that is, 6 volts I below the cathodepotntial.The circuitef Fig. 1, tube 8 being substituted for tube 1, then pro Vduces" a high output potential 61 when signals a and b are both low, anda low output p'otential in the other three alternative cases, thus:

The conductive state in the last ,three .case s i s attributable to thefact that when input signals -e1 and 62. are combined,- they produce ag'rid voltage of 10 v. which is. more ,positive' than? the'cut-ofi?voltage, +18 v., and when the "input signals are both atthelevel of anor 0 volts, th 1 tube is also conductive. 'Butth e cut-oifcorrdni tionis only obtained when both input signals are at the level of 62. Only inthis case is'the output signal delivered at voltage e1.

The circuit arrangement shown in Fig. 3 is one for producing an outputsignal-e1 or e2, which distinguishes between the resultant input voltageabove and below the cut-ofl point, when that resultantis the average ofthree or more simultaneously applied input signals each having one "orthe other of two values 61 and c2.

The cathode" of tube 9 may be grounded, or, through switch l0, it mayreceive a negative bias the value of which will depend on the cut-oil?bias that is needed to obtain a desirable distinction between theresultants of simultaneously applied signals, a, b, c, n, where someresultants are above and some resultants are below the cut-01f voltageapplied to the grid.' The grid potential will, of course, be the averageof potentialsei and/or e2 as applied by signals a, b, c, n, providedthat the parallel grid resistors H' are of equal value, as is preferred.

The values of components in the circuit of Fig. 3' to be chosen foroptimum performance are, to-a considerable extent, concerned with the D.C. gain characteristic of the tube that is used.

The D. C. gain is one of the factors'that will determine the number ofvariables or inputs that can be combined and impressed upon the singlegrid of a triode with positive discrimination or selection by the 'tube.So the gain, and hence the total number of variables that may becombined is at least partly dependent on the value of resistors" 2, 3,and 4, and the proportioning of these resistors each to the others.

The optimum selection of these resistor values is also one whichprovides for suitable transient response as well as for delivery of anoutput signal e1 only when the rid voltage is below that of cut-ofl 60.Assuming that it is required to obtain a plate rise time of about 5microseconds, then it follows that a v'alue'of 18,000 ohms for the plateresistor would be suitable. Given then the requirement of- 18,000 ohmsin theresistor 2, we'cho'o'se the values of the other resistors 3 and 4so as to provide the maximum gain.

-It will be noted that'theresistance 18,000 o of volts, is impressed onthe output lead 5, this lead being tapped off of the mid-point of thevoltage divider between +100 v. and 100 v. Also, when tube 1 isconducting its anode potential is lowered to a value which gives e2='2ov., as the output potential on lead 5. 1

The output circuit resistor values for resistors 2, 3, and 4, as statedabove, are a satisfactory compromise between the low current desirablein thewvoltage divider at cut-off condition and low time delay due tothe charge and discharge of interelectrode and stray capacities.

The circuit arrangement of Fig. 3 is theoretically. capable of use tocombine a plurality of (n) inputs each having a value e1 or e2 volts andto give a single output voltage also having one Or the other of the samevoltages depending upon whether the tube is or is not driven to cutoff.

Assume a plurality of 11. inputs, that is, a plurality of variablevoltages or potentials, a, b, c, n, each of which will have either thehigh value e1 or the low value e2. Further assume that at some instant acertain number It 6 of these inputs will be high. Then the remainder ofthe inputs :i or 12-71. will be low. As in Fig. 1, the inputs (binaryvariables) are connected through resistors ll of equal value to thesingle grid oftiiode tube 9. The input coupling is in effecta'potentiometer of which the tapping is on' the grid. If, of these,inputs h are assumed to have high values (0 volts) then 7" or n-h willhave low values (-20 v.) at the same instant. Assume that the cathodeisgrounded, as when switch I0 is setin the-position shown. Otherwise thecircuit components of Fig. 3 are the same as described in connectionwith Fig. 1.

,*When each of the resistors II has the same value R as previouslystated, then the instantaneous input grid voltage Xi may be expressed i=2+( 1 2)fi. h j But since h+:i=n and since all resistors I I havetlie1same value R, Formula 1 can be simplified thus:

I i= 2+( i- 2)' .The following table shows certain speciiic values forX1 when el=0 volts and 182=20 v.,' Formula 2 being used:

Number of Number of Inputs e1 Inputs e; (volts) 0 n 20 1 n-1 20 2 11-220 1 3 n3'- 20 1 nl 1 -20 3 And when n=3 for example:

Number of Number of Inputse Inputs a; (Volts) Now the tubecharacteristics and the values of the voltage divider sections can be sochosen that the cut-off voltage will fall between any two of the n+1possible voltages on the grid. But a simpler way to adjust the circuitfor a desired discrimination is to set switch I0 over to the right asshown in Fig. 3 and to supply a suitable negative; bias to. the cathode.Difierent values of negative bias will produce different outputresponses, as will be apparent. Thus if the output: is to be ez onlywhen all the input voltages are-gel, then the cathode should begrounded.

negative bias to be applied to the cathode, assuming that 11:3, as inthe above table, should be approximately 10 volts so as to discriminatebetween h=2 and h=1.

' ance values for the resistors I I.

other associated circuits is thereby minimized, al-

'found that, using a tube of the type 12AU'7, the

circuit operates reliably when n=3. It is known, however, that .1; couldbe a greater number and still retain the reliability of operation. Theincrease in the number of inputs should, however, be accompanied by theadoption of higher resist- Feed back from though speed of operation mayhave to be sacrificed in certain cases. If any other tube is to be usedfor this type of circuit it can be seen that the maximum number ofresistorsto the grid is limited by the ratio of output voltage swing tocut-ofi bias value.

It should be mentioned here that the ohmic value to be chosen for theinput circuit resistors I I is dependent on the magnitude of the load inthe output circuit. Undesirable feed-back conditions are, however, foundto be avoidable either by choosing input resistor values which lie abovecertain minima in respect to a given number m of different loads of unitwattage, or else by the adoption of a suitably greater power supplyvoltage.

To be more specific regarding the subject of the preceding paragraph, ithas been found experimentally'and mathematically that when the output ofone of our typical building blocks as above described is fedsimultaneously to the inputs of several other such building blocks, thefollowing minimum ohmic values tor resistors II must be recognized,where m represents the unit load value of each of the parallel-connectedbuilding blocks? to which the output of a first stage circuit is fed:

Minimum value of 11 4 ohm's 50, 000 3 112, 000 4 170, 000

the voltage divider sections are of the ohmic values shown in Fig. 1,also-when there are just two input resistors connected to each buildingblock unit.

In certain uses for the circuit of Fig. 3 it is necessary that-theswitch I be thrown to the right so that the-negative bias applied to thecathode shall assume a value such-that the tube 8 conducts when any oneor more of the 41 inputs is er and is cut-01f only when all inputs are62. The negative bias on the cathode may in this case be easily adjustedto give the desired discrimination. Fig. 4 shows one way by which alurality of tube circuits of our building-block type may be combined.Here there are at least two triode tubes I2 and I3 having theiranodesintercone nected so that they share in common the voltage dividersections '2, 3, and 4, and the common outputlead 5. Tube I2 has its gridsubject to 'control from two input signal sources a and b,

whiletube I3 has its grid similarly controlled from two other inputsignal sources 0 and d. An

. nth tube I31; is also shown having more than two independent inputcircuits. Additional input signal sources may also be connected to thegrids of tubes 1 2 and I 3 if desired.

When the circuit of Fig. 4 is limited to tubes I2 and I 3 it will beapparent from the foregoing description that the four input circuits ofFig. 4 result in an output that will be high only when both tubes arenon-conductive, i. e., in any case except when only a and b aresimultaneously high or when only 0 and d are simultaneously high, orwhen all four are high. When an additional tube or tubes including tubeI311 are used, it is generally the case that a low output potential willresult when any or all of the tubes are conductive, and a high outputpotential will result when all and only all of the tubes aresimultaneously non-conductive.

Fig. 5 shows a circuit arrangement in which several of theparallel-connected tube pairs of Fi 4 are utilized. This circuit is wellsuited for obtaining the sum or difference between two binary numbers inone denominational stage or order of a calculator and for giving effectto a carry requirement as derived from a preceding stage. The componentsof the circuit of Fig. 5 willnow be described, after which the operationwill be explained.

.Tubes I2 to I! inclusive have their anodes and output circuitsconnected in pairs to voltage di- .vider resistors and output circuitsthe same as in Fig. 4. .All .of the cathodes of these tubes aregrounded. The grid resistors II are all of the same value. The commonpower supply has positive, negative and grounded neutral terminalsappropriately connected to terminals as labeled illustratively v.,ground, 100 v.) in Fig. 5. Tube I8 is a single triode used as aninverter and V has circuit components the same as tube I in the voltagesa and a areinterchanged. So like-= wise the voltages b and b areinterchanged if another trigger pair is actuated.

, Input circuits which carry signals a and b are 7 applied to the gridof tube I2. (Tubes I3and I4 are both subject to control by input signalsa and b. The conductive 0r non-conductive state of tube I4 is always thesame as that of tube I3 and for reasons presently to be explained.

By way of illustration, the operation of the circuit-of Fig. 5 will bedescribed with reference to its useas a digital adder. In the binarysystern, as well as in a coded decimal system, the sum a+b must be oneOr another of three different digital values, 0, l, or with a carry tothe next higher order. When a--0" and b=.0" the grid of tube I2 willhave the potential as (20 volts), as explained in reference to Fig. 1.-This tube will then be non-conductive. It will still be non-conductiveif a=l" and b=0, or if a=0 and b=1. Only when a=1 and 1);1" do we obtaina grid potential of e1'(0 volts) in tube I2 to cause conduction.

Now since tube I3 is controlled by the joint effect of potentials a andb, these having been defined as the inverse of a and b respectively, itfollows that when a=0 and b=0, the potentials of signals a and b willboth be at 0 volts and the grid of tube I3 will be driven 'suflicientlypositive to produce conduction in this tube. In eachof the otherconditions, as described in the preceding paragraph, the grid of tube I3will be at some potential below cut-off and this tube will not conduct.e

Under the conditions described in the two immediately precedingparagraphs, the common output circuit for tubes I2 and I3 will nowdeliver potentials as follows:

Digit Values: Voltages Item Sources Input Signals O t t" u pu on The Sum,Wire 19 va b Tube 12 Tube 13 o 1 553 g e1 1+i n+ I P, 2 .2 I 1 10 .6161 2 The operation of tubes I2 and I3 does not.pro-. vide a result bywhich the digital sum 0+0=0 can be distinguished from 1+1=0 with carry,

.althougha't-entative value .is given forjthe units digitlin thedenomination to which the circuit applies. Usually a binary adder mustdeal with: multi=digit 'numbersand, therefore, must take care of.carries from a lower order and to .a higher-order. The circuitof Fig.includes the meansfor doing this. 1

- Triodetube I8 is simply an inverter. i Its grid" is controlled by theoutput signalion conductor I9,'this being a potential s whichrepresentsthe tentative sum a+b.. The potential 8 onoutput conductor 20'of tube I8represents the inversion of Weare now required to add a carrysignal, if any, Fascoming froml'a lower digital order, of the binary.computer.'.l Let or represent such av carry signal" and 'C'i willrepresent the inversion of that signal. I The potential ci=e1=0voltswhen' it"repres'ents the binary numbe'rfl, and at the 7 The pair oftriode tubes I6 andl'lis-u'sed toj obtain an output signal: representingthe units digit of a binary sum s+cr=Sowhere s and c are, as definedabove and where So is the wanted po-' tential for indicating thesummation u+b+c only as regards the digital order to which-thecircuit.:-applie s.

. ;The g rid of tube 1 e ubject to joint control by potentialslif andci,'whereas the'g'rid of mine" 1:1 "is sub ctedoint control bypotentials s am 10 01. There are only four possible permutations ofthese potentials due'to the fact that s" is the inversion of's, and ciis the inversion of 01. So the results derivable from the operation oftubes I6 and Il may be tabulated thus:

Digital Voltages of Input Signals RNumbersd O D eprescntc utput on igiTube 16 Tube 1' Wire 21 Value So,

a c; s a; I s c;

( 0 I 0 *6 F31 2 62 e1 0 (2) l 0 e e e1 e e1 1 (3) 0 1 e; .62 e e1 e1 11 1 2 2 "61 "81 ea 0 In the above table the asterisk 0) has been appliedto the combination of high input signals which renders a tubeconductive. Under all other conditions the tubes are non-conductive.Furthermore, if either one alone of the tubes I6, I! is conductive, thecommon output potential is e2. Both tubes must be simultaneously nonconductive in order to deliver the output signal e1. p I

Tubes I6 and II, like tubes I2 and I3 are only intended to produce theunits digit of a summation. So the determination of an output carrysignal is left to be obtained by the use of still another triode tubepair I4, I5. Tube I4 is subject to joint control by potentials at and bwhich are the inverse of the digit representationsa and 2;. Tube I5 issubject to joint control by the tentative sumrepresenting potential sand by, potential c'i which is the inversion of the income ing carrysignal. Atabulation of possible permutations of these potentialsfollows:

l sl'umbers ame as Conductive 111 Above voltage Values of State VoltageD Tables Output on Wire C T'b T b 22 I In I I u e u e a b c. a. b s c 1415 a 0 0 0 81 01 e: 81 i 0 (1) {O O 1 61 e1 6: ea 6: O {1 0 0 61 C1 61e1 2 o l 0 1. e e e1 e1 e1 1 0 1 0 81 6g 61 81 61 0 0 1 1 61 81 6 2g 811 (4) l l O a; e; e: 1 51 1 l l l e; e; e; 82 e l To summarize theoperation of the circuit of Fig. 5 it should be observed that in onebinary digit stage ofa multi-digit adder the augend and addend signalsare caused to control tubes I2, I3 and I4. The commonoutput s from tubesI2 and I3 is applied directly to tubes I1 and I5 .for partial controlthereof, and issubjected to an inversionprocess in tube I8, giving s.Tube I6 is subject to joint control .by, output s from. tube I8(representing the inversion .of the summation signal 5) and by theinversions; ,of a

carry signal 01 which is brought in from a lower denominational order ofthe adder. .Tube I1 is jointly controlled by said carrysignal c1. and bythecommon .output 3 fromtubes". I2, and. I3. Hence the functionperformed bytubes I6 and I! in combination is to deliver a signal Sowhich {represents the units digit of the summation The ordinal carrydigit Co of the same sum-1 mation a'+b'+ci is what we obtain from thecommen-output circuit of tubes'I4 and-I5. This is, true 'becausaloolsing at the table last above.

' sult of making both tubes [4 and I5 nonconductive at the same time.

Considering further the eight different permutations of three numbers tobe added, the carry signal 00:0 (in effect -no carry) occurs in the fourcases where one or the other of the tubes 14 and I5 are conductive,representing a summation not greater than 1. Hence the significance ofthe Cu signal is obtained irrespective of the value of signal So. Thesummation expressed as a two-digit binarynumber may, therefore, beproperly represented by Co and So as 00, 01, 10-, or 1 1, these beingthe four po'ssible results of adding a lowerorder carry to the sum oftwo binary digits ofa particular denomination. 7 v I It will beunderstood by those skilled the art, in view of the foregoingdescription orseveral illustrative embodiments: of our invention, thatvarious modifications and comb'inations'oi our building block units, anddifie'rent'mefnbers of the same, can readily be assembled for meetingthe requirements of difierent complex switching operations. What isparticularly stressed as a novel feature of our inventionis thatourbasic building block circuit can be so concatenated with othersimilar circuits "as to maintain equality offvoltage swing between the"input to. one stage and the input potential applied to asucceedingstage, thus enabling us to maintain this same equality withoutappreciable departure from a chosen range between high and low signalpotentials, even where numerous stages are involved.

it will also be appreciated that the utility of our basic building blockcircuit is not confined to electronic devices for performingmathematical computations. Thus, if we substitute any statements as usedin symbolic logic for, the information which distinguishes between 0 andl in the binary numeral system, we find that the building block circuitas herein shown is still useful without any modification. .So, generallyspeaking, it is proposed to construct various embodiments of electronicswitching systems out or these basic building blocks for the "purpose ofperforming switching operations of a more or: less complexnaturerandpa'rticularly to acc'emplishj the desired results with "aminimum of tube and. other circuit components. Also; in order to achievehigh speed performance dependability of control 7 it has been found thatthe 'hereinfdisclose'd switching circuit-has numerous advantages overcircuits known that were used for similar purposes,- 1

1. A basic electronic switching circuitifondelivering one or theotherjoftwo output voltages each dependent upon the input voltagessimultaneously applied to ,the single grid ofja mace discharge element,sai'd circuit comprising i'sa'id discharge element, resistors of. equalvalue Jean allel-connected to said grid and each "car yin'g a distinctone of said input voltages asideveloped with respect to the cathodeofs'aidelernent,

a direct current source having a th'reejse tion voltage dividerconnected'across'itsgposit negative terminals. an "anode cbnnectionto.the

previously 12 junction between the two voltage divider sec tions whichare positive with respectto the third said section, an output leadconnected to the positive end of said third section, and means includingsaid voltage divider,the respective values of its sections beingsuitably chosen for operative functional performance, whereby there isdeveloped on said output lead a voltage which, with respect to a fixedpotential, has one or the other of two values correspondingsubstantially to the high and low values of said distinct inputvoltages. I Y

2. A basic switching circuit according to claim 1 and including meansfor so adjusting the cut off biasof said element as toobtain'a desiredpoint of separation :between high and low output voltages which resultin one case from the coin:- cidence of input voltages of suflicientlynegative value to efiect a non-conductive state in said element, and inanother case from the coincidence of input voltages of sufficientlypositive value to effect conduction in said element.

3. In combination, a, plurality of basic switching circuits, such asdefined by claim 1, and constituting concatenated stages, the outputlead from one stage being operative to deliver an 'input voltage to asucceeding stage. r

4. A basic electronic circuit as defined in claim 1 and including meansfor applying simultaneously to the grid, of said device signalpotentials from three or more independent sources, each potential havingone or the other of two values c1 and c2 and the grid being normally sobiased with respect to the cathode as to efi'ect discrimination betweentwo predetermined ranges of grid control potentials, one said rangebeing to render the :device conductive and the other range being torender the device non-conductive.

5. A basic electronic circuit for respondng to either of twosimultaneous transient conditions, said circuit comprising an electrondischarge device of the triode type, resistive connections of equalvalue' parallel-connected in input circuits between the grid and cathodeof said device, each of. said connections including separate signalacteristics of said device as .to effect'an output voltage having one orthe other of. two predetermined values depending upon the state ofconductionor non-conductionin said device, said output voltage. valuesbeing substantially the same asthe high and low values respectively ofany of said transient condition-representing po"-.

' tentialsc. A basic electronic circuit as definedinrclaim 5 incombination with an electronic inverter device, whereby the relativepolarities of the out.-

put potentials are reversed.

7. An electronic switching device for produc ing discriminatory effectsin response tothe joint-control of said deviceby simultaneouslyappliedinputsignals from 'a plurality of independent potential supplies,each of the signals being alternatively deliverable at onejor the otherof I two predetermined" potentials with 'respectto ground potential,said device, comprising a'siiigle' triode' discharge tube poweredbya"direct current source, :gan. anode resistor connected from. .lihe

positivev terminal 1 ct ,said source to the anode of said ,tube,..a.connection i om in erm dia an:on said, sou ce. a e a seround pote t al.to the cathode of said tube, a two-section voltage divider connected atone end to the anode oi'saidtube and at the other end-to the negativeterminal of said source, a utilization circuit connected between thejunction point of said voltage divider sections and ground, resistors ofequal value connected between the controlgrid oisaid tube' and eachof'said potential supplies respectively, and means includingsai'd'a'no'de resistor and said voltage divider for-causing the outputpotential to be maintained at one or the-other of two values eachcorresponding respectively to the high and low voltages of said inputsigother.

10. An electronic computer stage for obtaining the sum of two binarydigits and for combining therewith an incoming carry signal, theoperative result being to deliver two output signals one of whichsignifies the primary digit value of the summation of said two binarydigits plus the value of said incoming carry signal and the other ofwhich signifies the value of an outgoing carry signal applicable to astage of higher denominational order, said computer stage comprising apair of triode discharge tubes having their anodes interconnected andsupplied with anode potential through a common anode resistor, theoathodes being grounded, means for applying augend group 10. 35;

:14 ut .signals respectively,- i neda r s. fir t ab ve. m n

s liiria v; nu bers cc n i ne, a s rat sta for each denominationalorder, each stage coni- 'n eingrrepit sentative,of the its d it of a,

(lei ices ident cal-w h res QttQthefirst roup ndavoltag inve ter sub t.tov o i rol byout .p tfir mih first group, means inherentinthe st c urlo th se ondv ro n. tor.v producingaan output voltage representative ofthe units digit of a final sum which reflects the addition of acarryover digit to said tentative sum, the voltage representing thiscarry-over digit being derived from a preceding stage, and the voltagesrepresentative of the tentative sum being applied directly from theoutput of the first group and simultaneously from said voltage inverter,and means inherent in the structure of the third group for so combininginput voltages derived 'from (a') the source of those first abovementioned, (1)) the output of the first group and (c) a voltage which isthe inverse of said voltage representing carry-over digit, that theoutput from the third group is representative of a carry-over digit tobe taken into a higher order stage.

12. An electronic switching circuit comprising at least two triodedischarge elements having their anodes interconnected, a voltagedividerhaving three sections, the most positive of which is connectedbetween said anodes and the positive and addend signals simultaneouslyto the grids v of said tubes, the augend signal when applied to the gridof one tube being of a polarity which is the inverse of the augendsignal applied at the same time to the grid of the other tube, theinverse relationship of signal potentials being also characteristic ofthe addend signals, a voltage divider connected between the anodes ofsaid tubes and a direct current source terminal which is more negativethan the cathodes of said tubes,

an output circuit connection at an intermediate point of said voltagedivider, means for inverting the sense of the output potential of saidintermediate point, ,a second pair of triode discharge tubes havingcircuit parameters corresponding to those of the first pair, one tube inthis second pair being subject to joint control by an output signal fromsaid sense-inverting means, and by the inverse of an incoming carrysignal, the other tube in said second pair being subject to jointcontrol by the direct output from said first pair and by said incomingcarry signal, a third pair of triode discharge tubes having circuitparameters corresponding to those of the first and second pair, one tubeof this third pair being subject to joint control by the inverse of saidaugend and addend signals respectively, and the other tube in said thirdpair being subject to joint control by direct output from said firstpair and by the inverse of said incoming carry signal, the functions ofthe second and third pairs being to deliver the two terminal of a directcurrent source, the intermediate and most negative sections beingserially connected to the negative terminal of said source, an outputcircuit connected from the junction point of the last mentioned sectionsto a point of fixed potential, means for fixing a common cathodepotential intermediate between the potentials of said direct currentsource terminals, and a plurality of input circuit resistors ofequalvalue connected to the grid of each triode element, and in circuitbetween said grids and cathodes of said elements, each said grid beingsubject to joint control by signal potentials separately applied throughat least two of said resistors, and each of said signal potentialshaving either one or the other of two predetermined values dependingupon their significance, said switching circuit being furthercharacterized in that it is enabled to deliver an output potentialsubstantially equal to the high voltage limit of said input signalpotentials whenever all said discharge elements are non-conductive, andto deliver an output potential closely approximatin the low voltagelimit of said input signal potentials whenever any one or more of saiddischarge elements is rendered conductive.

13. A basic electronic switching circuit including a triode, a pluralityof equal resistive elements parallel connected to the grid of thetriode, each having a high potential at or a low potential b" appliedthereto, said elements combining said potentials to cut off or allowconduction of the triode, a source of DC potential having positive andnegative terminals, and a voltage divider connected between saidterminals and having a center tap, the anode of the triode beingconnected to the voltage divider on th positive side :dfthe enter438:1); and the vdl'tsige-divider values "being s uch vtihat the centertap thereof assumes "bmbining said pbtenti'l's tocut 'dfi dr'aslllow-conauction of the tri6de,-'a sourceof DC"pbtenti'2;1 qiavm positive andnegative terminals. and a ithie section voltage divider having a ceritertap between the negativemost section and the 'other two, the anode f thetriode being connected to et er stages: e r

v A BEPA W sate-

